Cycloolefin monomers (cycloolefins) which contain a norbornene group are known to polymerize by ring-opening polymerization and addition polymerization. Polymers obtained by ring-opening polymerization of cycloolefins that contain a norbornene group are well known. For example, U.S. Pat. Nos. 4,136,249; 4,178,424; 4,136,247 and 4,136,248, assigned to the same assignee of the present invention, describe such polymers, and each is incorporated herein by reference for the description of polymers therein.
Ring-opening polymerization of cycloolefins yields unsaturated linear polymers which are of particular interest in that they are known to be reactive (sulfur-vulcanizable) and they are known to exhibit attractive property profiles with good heat distortion temperatures for many polymer applications, such as, for example, as automotive parts, particularly body panels, bumpers, facia, etc. Many of these polymer properties, such as heat distortion temperature, are dependent on a high degree of conversion of the cycloolefin monomer into polymer. This is particularly true in bulk polymerization processes where any unreacted monomer will remain dispersed in the finished article, providing an undesired plasticizing effect and/or this unreacted monomer may leach from the molded part, rending the finished article less useful. It is known a substantially pure feedstock of cycloolefin monomers will help provide a high degree of conversion in bulk polymerization processes, and may often be necessary to provide useful finished articles. A cycloolefin monomer feedstock of over 99% purity is often desired in RIM techniques, which is a common example of a bulk polymerization process.
Dicyclopentadiene is a common cycloolefin monomer used to prepare ring-opening polymerized polymers. Recent U.S. Patents directed to dicyclopentadiene polymers include U.S. Pat. Nos. 3,778,420; 3,781,257; 3,790,545; 3,853,830 and 4,002,815. Dicyclopentadiene monomers are by-products in ethylene production and are commercially available in different grades of purity. The commercial crude grades of 97% to 98% dicyclopentadiene do not yield the rapid reactions nor high conversion desired for ring-opening polymerization. The more costly 99% pure dicyclopentadiene shows the necessary quality for both high activity and high conversion. It is desirable to develop a simple means to enhance the polymerization activity of the less pure dicyclopentadiene grades to provide the desired activity and conversion.
Purification of other cycloolefin monomers for use in ring-opening bulk polymerizations is also desired. For example, norbornene (bicyclo(2.2.1)hept-2-ene), substituted norbornenes, tetracyclododecene, substituted tetracyclodocenes, and higher homologs of these with cyclopentadiene, are known to be produced by the Diels-Alder reaction of cyclopentadiene and selected olefins. Often a mixture of products is obtained from these reactions, requiring purification. A less costly purification process would be a great advantage in utilizing the cycloolefin monomers synthesized from dicyclopentadiene.
In copending application, Ser. No. 122,849, filed Nov. 19, 1987, heat treatment of a polymerization grade cycloolefin feedstock was found to yield a product containing cycloolefins with increased molecular weight. The heat treatment did not affect the reaction rate or the degree of conversion of the monomers. The monomers were still of polymerization grade after heat treatment.
It has now been discovered that the heat-soaking porcedure (or heat treatment) of commercial crude grade 97-98% pure dicyclopentadiene enhances its polymerization activity by reducing the quantity of polymerization retarding impurities. This treated crude dicyclopentadiene provides the rapid polymerization rates and high monomer conversation desired from the high quality, commercial polymerization grade, 99% pure dicyclopentadiene.